The "radio modem," i.e., a selective call receiver having a data interface for communicating with an external computer, is well known in the art. An example is the NewsStream.TM. Advanced Data Receiver manufactured by Motorola, Inc. of Schaumburg, Ill. This radio modem is intended for use with computers having an RS-232 port and a telecommunications program that supports a popular file transfer protocol called "XMODEM." Coupling the data interface of the conventional radio modem with such a computer allows the computer to receive information transmitted by radio and addressed to the radio modem and to store the received information in a file. Additional file access or other software is required when a user then wishes to examine or work with the information in the file.
While the conventional radio modem provides an excellent method of receiving information in a portable computer, the application software available for most portable computers does little beyond displaying information received and perhaps doing a name or telephone number look-up based on information received through the radio modem. Application software for providing vertical services that are custom tailored to the needs of various users is becoming available, but at a relatively slow pace.
An obstacle to development of vertical application software for the conventional radio modem is the lack of a consistent, high-level application interface that will remain unchanged from one brand of external computer to the next and from one model of radio modem to the next. This lack of consistency occurs because the conventional radio modem requires the application program to provide low-level drivers that are unique to each type of external computer. The low-level drivers also necessarily must be changed in response to subsequent changes in the design of the radio modem, e.g., changing from a serial data link to a parallel link between the radio modem and the external computer, or modifying low-level proprietary commands in the radio modem to add new features.
Thus, what is needed is a way of providing a consistent interface between the application software and the radio modem to facilitate the development of new and more powerful application software to support vertical services. A radio modem is needed that expands the functionality between the application software and the radio modem and that provides a consistent application programming interface from one type of external computer to the next. A radio modem that contains built-in application programs custom tailored to support a variety of user requirements is also needed.